1. Field of the Invention
This invention relates to an industrial furnace provided with rotary regenerative burners for utilizing the heat of the exhaust gas resulting from combustion for heating an oxidizing agent.
2. Description of the Prior Art
Such industrial furnaces as pipestill heater and iron and steel furnaces frequently adopt heat recovery type combustion devices adapted to utilize the heat of the exhaust gas resulting from combustion for heating an oxidizing agent.
Among these combustion devices is included that which is disclosed in Japanese published applications JP-A-1-222,102 and JP-A-4-101,191, for example. This combustion device has attached to the wall of the combustion chamber of an industrial furnace a regenerator formed of a regenerative material and adapted to manifest perviousness to a gas and has a duct part communicating with this regenerator. This duct part has formed therein an oxidizing agent duct for passing an oxidizing agent and an exhaust gas duct for passing the exhaust gas resulting from combustion. Then, the oxidizing agent duct is provided therein with an oxidizing agent path for passing the oxidizing agent and the exhaust gas duct is provided therein with an exhaust gas path for passing the exhaust gas resulting from the combustion in the industrial furnace. The heating of the oxidizing agent is attained through the regenerator heated with the exhaust gas by rotating the regenerator and the duct part relative to each other.
The term "oxidizing agent" as used herein refers generally to oxygen atom-containing gases such as pure oxygen and nitrogen oxide and oxygen gas-containing mixed gases such as air and oxygen-enriched air.
This combustion device itself is designated as a rotary regenerative burner. Since it is adapted to heat the oxidizing agent while keeping the regenerator in rotation, it is simple in construction as compared with a combustion device which requires a heat exchanger for a heat recovery to be separately provided exclusively for the purpose of heating the oxidizing agent. It is quite effective in saving energy because it enables the oxidizing agent to be directly heated with the regenerator made of heat-resisting material such as ceramics which is heated with the hot exhaust gas.
Incidentally, this rotary regenerative burner accomplishes exchange of heat between the exhaust gas and the oxidizing agent by relatively rotating the regenerator or the duct part by means of the power such as of an electric motor or a pneumatic motor. It can no longer attain the exchange of heat when the rotation of the regenerator or the dust part is stopped. As a result, the exhaust gas which has an elevated temperature flows out through the same flow path of the regenerator. In the worst case, the escaping exhaust gas will possibly reach a temperature exceeding the heat-resisting limits of such parts as an induced-draft fan and a control valve which are disposed on the downstream side of the rotary regenerative burner and damage them quickly.
Further, in this industrial furnace, the combustion chamber is in a substantially closed state and the regenerator part alone is capable of releasing the exhaust gas out of the combustion chamber. In case of an accidental stop of the relative rotation mentioned above, therefore, the combustion can be continued as an emergency measure by using air at ambient temperature. Then, the rotary regenerative burner Works in the same way as any conventional burner and the exhaust gas is no longer aspirated by the rotary regenerative burner and the preheating of the oxidizing agent is no longer continued.
An effort to keep the amount of heat transfer constant while continuing the combustion with air at ambient temperature as an oxidizing agent, therefore, necessitates an increase in the amount of combustion proportionate to the amount of the oxidizing agent to be consumed for preheating.
When the amount of combustion is increased as described above, the amount of the exhaust gas is increased in direct proportion to this increase in the amount of combustion. Since the inner pressure of the furnace is suffered to increase unless the induced-draft fan is enlarged to increase its capacity, the introduction of the oxidizing agent is obtained only with difficulty. In the worst case, an accidental fire will possibly occur.